Wave & Electromagnetic Spectrum Notes

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Wave Electromagnetic Spectrum Notes

• March 3, 2013

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I.) Properties of Waves

• Wave A periodic disturbance in a solid, liquid
  or gas as energy is transmitted through a medium
  ( Waves carry energy b/c they do work)
• Waves create wave fronts (circles) that
  have the same amount of total energy but as the
  circles get larger the energy spreads out over a
  larger area.

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• 1) Mechanical Waves waves that require a medium
  through which to travel
• a) Medium physical environment in which
  phenomena occur
• 1) Example water, air, Earth
• b) Almost all waves are mechanical waves,
  except EM waves

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• 2) Electromagnetic Waves waves that consist of
  oscillating electric and magnetic fields, which
  radiate outward at the speed of light (3.0 x 108
  m/s) (Holy Gazoli! Thats fast!)
• a) Example visible light, microwaves, etc.
• b) DO NOT require a medium

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• Fun Wave Vocabulary Ha! Ha!
• A) Crest section of the wave that rises above
  the equilibrium position
• B) Trough section which lies below the
  equilibrium position

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• C) Wavelength distance between one point on the
  wave and the nearest point where the wave repeats
  itself
• 1) This can be measured from crest-to-crest,
  trough-to-trough, or from the start of a wave to
  the start of the next one.
• 2) Symbol for wavelength is ?

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• D) Amplitude maximum displacement from the
  undisturbed position of the medium to the top of
  a crest.

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• E) Period (T) time required for one wave to
  complete one full cycle of its motion
• i.e. The period measures how long it takes for
  a wave to pass by
• 1) Example From its highest point to its lowest
  and back again
• 2) Measured in seconds (s)

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• F) Frequency the number of complete waves that
  pass a point in a given time. It has the symbol
  f.
• 1) SI Units Hertz (Hz)
• 2) Hertz units measure the number of
  vibrations per second
• ex. 1 vibration per second is 1 Hz, 2
  
• vibrations per second is 2 Hz
• 3) Period is related to frequency in that the
  frequency is the inverse of the period

Frequency 1 / period f 1 / T
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• G) Wave speed
• 1) The frequency and wavelength are related to
  one another and to the speed of the wave by the
  following formula, where v is equal to the
  speed
• Speed Wavelength x Frequency
• v ?f

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II.) Traveling Through Mediums

• A) Mechanical waves require a medium in order to
  travel through
• 1) Waves are classified by the direction that
  they travel through the medium
• a) Transverse Wave
• the particles in the
• medium move
• perpendicular to the
• direction wave is traveling
• 1) Ex Light waves

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• b) Longitudinal Wave the particles in the
  medium move parallel to the direction the wave is
  traveling
• 1) Ex Sound waves

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• C) Surface Wave- occur at the boundary of 2
  different mediums (ex. Water and air)
• Particles in a surface wave move both
  perpendicular parallel to the direction the
  wave travels
• The up/down motion combine w/ the side to side
  motions to produce a circular motion overall
• Ex. Ocean waves

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• 2) Speed and direction of these mechanical waves
  are affected by the medium they encounter
• a) Example Sound waves travel very fast through
  air, but they travel 3 to 4 times faster under
  water
• 1) why so many animals use sound waves to
  communicate (dolphins)
• b) They travel even faster in a solid, producing
  speeds 15 to 20 times faster in rock or metal.
• Speed of sound waves in types of mediums
• (slowest to fastest)
• Gas ? Liquid ? Solid

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III.) Doppler Effect an observed change in the
frequency of a wave when the source or observer
is moving

• A) Pitch of a sound (how high or low it is) is
  determined by the frequency at which the sound
  waves strike the eardrum
• 1) When an object that is emitting sound waves
  (i.e. ambulance) is at rest, the sound waves
  spread out in circles and anyone who is standing
  near the object will hear the same pitch

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• 2) When an object that is emitting sound waves
  (i.e. ambulance) is moving however, the waves are
  closer together in the direction of the motion.
  So if one person is standing in the same
  direction as the motion, the pitch will seem
  higher than if a person was standing in the
  opposite direction

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IV) Wave Interactions

• A) Reflection the bouncing back of a ray of
  light, sound, or heat when the ray hits a surface
  that it does not go through
• B) Refraction the bending of waves at an angle
  when they pass from one medium into another
• 1) Ex Spoon in glass of water appears to be
  broken because the light waves are bending at a
  different angle when they enter the water versus
  the air

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• C) Diffraction The bending of a wave when the
  wave finds an obstacle or an edge, such as an
  opening
• 1) Waves will bend around an object or opening
• a) Example hear sounds clearly from classroom
  only through open door because waves spread out
  into the space beyond the door

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• D) Interference
• 1) Constructive Interference when two waves
  interact and the resultant wave has a larger
  amplitude (Part A)
• 2) Destructive Interference when two waves
  interact and the resultant wave has a smaller
  amplitude (Part B)
• HOW LOUD A SOUND IS DEPENDS UPON THE AMPLITUDE
  OF THE WAVES THAT INTERACT!!

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• Standing wave- can form when a wave is reflected
  at the boundary of a medium.
• Interference occurs b/w the original wave the
  reflected wave
• Causes wave to vibrate in a stationary pattern
  (resembles loops)
• Looks like wave is standing still but it reality
  waves are traveling in both directions

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• Standing wave components
• Nodes- point that has no vibration separates
  the loops of a standing wave (lie where the crest
  of original wave meets the trough of reflected
  wave
• Antinodes- point of maximum vibration form where
  the crests of the original wave line up w/ the
  crests of reflected waves

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Electromagnetic Spectrum NotesI.)
Electromagnetic Waves

• A) What are EM Waves?
• 1) How are they produced?
• a) Electric and magnetic fields are constantly
  changing
• b) EM waves are produced when electric charges
  vibrate or accelerate

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• 2) How they travel
• a) Since electric and magnetic fields are
  constantly changing, they regenerate each other
• b) EM waves can travel through a vacuum (empty
  space) as well as through matter
• B) Speed of EM waves
• 1) Michelson (1852-1931) setup an experiment to
  try and find how fast light travels
• 2) Speed of light in a vacuum, c3.00x108m/s

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II.) Electromagnetic Spectrum

• A) The Waves of the Spectrum
• 1) EM spectrum all of the frequencies or
  wavelengths of electromagnetic radiation
• 2) The EM spectrum includes radio waves,
  microwaves infrared rays, visible light, UV rays,
  X-rays, and gamma rays.

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• B) Radio Waves
• -Longest wavelength
• -Lowest Frequency
• 1) Radio waves are used in radio TV
  technologies, as well as in radar.
• a) Radio
• 1) Amplitude modulation (AM)
• 2) Frequency modulation (FM)
• b) Radar
• 1) Send out short bursts of radio waves that
  bounce off objects return to receiver

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• C) Microwaves
• -Shorter wavelength than radio waves
• -Higher frequency than radio, but lower than
  infrared
• 1) Only penetrate food at the surface

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• D) Infrared Waves
• -Shorter wavelength than microwaves
• -Higher frequency than microwaves, but lower
  than red light
• 1) Infrared rays are used as a source of heat
  to discover areas of heat difference
• 2) You cant see infrared radiation, but your
  skin feels its warmth

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• E) Visible Light
• -Each wavelength corresponds to a specific
  frequency
• Color determined by frequency
• 1) People use visible light to see, help keep
  them safe, and to communicate with one another.

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• F) UV Rays
• -Shorter wavelength and higher frequency than
  violet light
• 1) UV rays have applications in health and
  medicine, and in agriculture.
• a) Helps skin produce Vit. D, can cause
  sunburn, cancer, and used to kill
  microorganisms

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• G) X-Rays
• -Shorter wavelength and higher frequency than UV
  rays
• 1) X-rays are used in medicine, industry, and
  transportation to make pictures of the inside of
  solid objects.
• a) X-rays are absorbed by solid objects
  (teeth, bones) so solid objects appear white

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• H) Gamma Rays
• -Shortest wavelength
• -Highest frequency
• 1) Gamma rays are used in the medical field to
  kill cancer cells and to make pictures of the
  brain in industrial situations as an inspection
  tool.